Question 180219
Substitute and get to an equation with one variable.
{{{5r-4s-3t=3}}}
{{{5(3s+1)-4s-3(s+r)=3}}}
{{{5(3s+1)-4s-3(s+(3s+1))=3}}}
You now have an equation only in s.
Now solve for s and go back to find r and t.
Repost if you get stuck or need more help.